1. Field of the Invention
The present invention relates to a charged-particle beam lithography apparatus and a device manufacturing method.
2. Description of the Related Art
An electron beam lithography apparatus as a type of charged-particle beam lithography apparatus has conventionally been developed with an aim to increase the throughput. An improvement in throughput requires increasing the exposure beam current, which faces a problem attributed to the Coulomb effect. The Coulomb effect has the demerit of blurring a convergent electron beam due to the repulsive force between electrons, resulting in degradation in resolution. For this reason, the resolution and the throughput have a trade-off relationship.
To increase the exposure beam current while suppressing aberration due to the Coulomb effect to a considerable degree, a method of decreasing the average density of the exposure beam current to some extent is available. This method reduces the Coulomb effect by decreasing the current density by irradiating an exposure region (subfield) as relatively large as about several hundred micrometers square, thus maintaining a given throughput.
Another method sets a relatively large convergent angle of an electron beam on the sample surface. This method applies a decelerating electrical field between the projection lens and the sample. It is expected to reduce the aberration of the projection lens, and to suppress a decrease in resist sensitivity and heat generation, and deterioration of the sample surface, by irradiating the sample surface with a charged-particle beam at a low speed.
Japanese Patent Laid-Open No. 2000-232052 discloses a scheme that reduces aberration by a decelerating an electrical field. The scheme disclosed in Japanese Patent Laid-Open No. 2000-232052 applies decelerating electrical fields between the transfer mask and the projection optical system, and between the projection optical system and the wafer in an electron beam exposure apparatus.
Although the method of decreasing the average density of the exposure beam current is applied to an electron beam exposure apparatus, it requires a transfer mask, which entails an additional cost.
In the method of setting a relatively large convergent angle of an electron beam, geometrical aberration increases as the exposure area (angle of view) increases. To attain high resolution, the aberration performance of the projection lens must meet a strict demand. Still worse, a disturbance of the decelerating electrical field occurs due to factors associated with, for example, the shape of the sample surface and a member disposed on the stage, so parasitic aberration and a positional shift of the charged-particle beam occur. The scheme disclosed in Japanese Patent Laid-Open No. 2000-232052 may cause a disturbance of the decelerating electrical field due to factors associated with, for example, the shapes of the wafer surface and its vicinity, and a member disposed on the stage, so parasitic aberration occurs, resulting in degradation in resolving performance.